1) $\frac{x}{5}$ =$\frac{4}{y}$ =$\frac{z}{-80}$ =$\frac{42}{105}$
<=> $\frac{x}{5}$ =$\frac{42}{105}$
<=>x=42.5 : 105=2;
vì $\frac{x}{5}$ =$\frac{4}{y}$
<=> $\frac{2}{5}$ =$\frac{4}{y}$
<=> y=4.5 :2=10;
vì $\frac{4}{y}$ =$\frac{z}{-80}$
<=> $\frac{4}{10}$ =$\frac{z}{-80}$
z=4.(-80):10=-32
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2) a) $\frac{15}{-24}$ ;$\frac{-50}{80}$ ;$\frac{65}{-104}$
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b) $\frac{15}{-24}$ ;$\frac{-45}{72}$ ;$\frac{75}{-120}$
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